Does anyone know a simple way to set the default working hours on Exchange/Office 365?

The company I am working for has mostly UK employees and I want to set the default working hours to be from 8:30am to 6:30pm in order to restrict room bookings to times when the premises are physically open. I know there is a PowerShell cmdlet (Set-MailboxCalendarConfiguration) that will set individual working hours which is fine but I’m not very experienced with PS at present so if there was just a place I could go to set them that would be better for now.

Something like Get-Mailbox | Set-MailboxCalendarConfiguration should do it
Build it up bit by bit- use Get-Mailbox and filter to get the list of users you want, then pipe it to the Set cmdlet

So PowerShell is the only way? Surely there must be somewhere in Admin Centre that would allow me to do it more easily .. besides, as I said above, I’m not very experience with PS (still learning it if truth be known).

There may be – I don’t use O365 enough to keep up with the changes in the admin interface. Can you set them per user in the admin centre – if so, try selecting users in bulk.
PowerShell is definitely the preferred way, and all SysAdmins should learn it (for self defence purposes :)).